In interferometric tomography, two-dimensional projection extraction, i.e., wave-front retrieval from interferograms, is a critical step for a successful three-dimensional reconstruction. We analyze the difficulty of locating the first-order frequency spectrum—a difficulty inherent in interferogram phase unwrapping by means of the traditional Fourier transform. The problem becomes more serious when we deal with interferograms obtained in real experiments, which usually lack exactly parallel and equally spaced references. To overcome this difficulty, we propose the method of localized matching filtration with Gabor filters and apply it, for the first time to our knowledge, to interferogram phase demodulation. A multi-channel Gabor spatial filter set is constructed to yield the optimally matched local spatial frequency. The optimization is aimed at maximizing the norm of the output of the filters. At the same time, noise and opaque objects are removed. The method, applied to both simulated and real interferograms, proves to be more effective and more flexible than the conventional Fourier transformation method, especially in cases in which references are not equally spaced and fringes are seriously deformed.
© 1999 Optical Society of AmericaFull Article | PDF Article
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